Abstract
Begomoviruses, belonging to the family Geminiviridae, are responsible for diseases causing significant damage to vegetable crops. Betasatellites, circular single-stranded DNA molecules dependent on begomoviruses for their replication and dissemination, increase the severity of diseases caused by begomoviruses. In the context of global food security, the emergence of begomovirus/betasatellite associations represent a real threat to the Mediterranean Basin, which is already infested by these viruses. The high risk of introduction of betasatellites into the region is exacerbated by the lack of information on the factors contributing to their maintenance in host plants and their spread into new ecosystems, thus limiting the possibilities for effective management of this risk. The work of my thesis aims to identify certain risk factors associatedwith the propagation of viruses and betasatellites. The research is presented in three chapters covering the following studies: 1)The study of the prevalence of begomovirus/betasatellite associations, allowing for the analysis of the impact of these new diseases at the scale of agricultural landscapes ; 2)The evaluation of the potential for vector transmission transfer of betasatellites to new virus/plant combinations ; 3)Exploratory work aiming to highlight how each element of the triptych (virus, betasatellite, host plant) can play a determining role in influencing the interaction between the other two protagonists.